1. Field of the Invention
The present invention relates to a thin-film magnetic head wherein a coil layer is formed between core layers. More particularly, the present invention relates to a thin-film magnetic head and a method of manufacturing the head, which enables an upper core layer to be satisfactorily formed, is adaptable for a narrower track width, and can improve an overwrite characteristic and suppress the occurrence of write fringing.
2. Description of the Related Art
FIG. 30 is a vertical sectional view showing the structure of a conventional a thin-film magnetic head.
The thin-film magnetic head of FIG. 30 is an inductive head for recording, which is disposed at a trailing-side end surface of a slider of a floating magnetic head, the slider floating in an opposed relation to a recording medium, e.g., a disk of a hard disk drive.
Numeral 1 denotes a lower core layer formed of a magnetic material such as an NiFe alloy. A gap layer 2 of a nonmagnetic material, such as Al2O3 (alumina) or SiO2, is formed on the lower core layer 1. An insulating layer 9 of a resist material or any other suitable organic material is formed on the gap layer 2.
On the insulating layer 9, a coil layer 4 is spirally formed using a conductive material having low electrical resistance, such as Cu. Note that the coil layer 4 is formed to surround a base end portion 6b of an upper core layer 6 (described later), but only a part of the coil layer 4 appears in FIG. 30.
The coil layer 4 is covered by an insulating layer 5 of, e.g., an organic material, and the upper core layer 6 is formed on the insulating layer 5 by plating a magnetic material such as Permalloy. A fore end portion 6a of the upper core layer 6 is joined to the lower core layer 1 through the gap layer 2 on the side facing a recording medium, whereby a magnetic gap with a gap length GI is formed. The base end portion 6b of the upper core layer 6 is magnetically connected to the lower core layer 1 through a hole formed in the gap layer 2.
The fore end portion 6a of the upper core layer 6 is formed such that its size in the direction of track width (X-direction as indicated in FIG. 30) is equal to a track width Tw. A recent trend toward a higher recording density requires the track width Tw to be reduced to a smaller value.
In such an inductive head for writing, when a recording current is applied to the coil layer 4, a recording magnetic field is induced in the lower core layer 1 and the upper core layer 6. Then, a magnetic signal is recorded on a recording medium, such as a disk of a hard disk drive, with a fringing magnetic field through a magnetic gap area between the lower core layer 1 and the fore end portion 6a of the upper core layer 6.
The upper core layer 6 of the thin-film magnetic head described above is formed by the so-called frame plating method. FIG. 31 shows one of successive steps for forming the upper core layer 6.
As shown in FIG. 31, after forming the coil layer 4 and covering the coil layer 4 by the insulating layer 5, an undercoat layer 7 of a magnetic material, e.g., an NiFe alloy, is formed over an area extending from an exposed portion of the gap layer 2 near a fore end of the head to the insulating layer 5.
Then, after forming a resist layer 8 on the undercoat layer 7, a pattern corresponding to the shape of the upper core layer 6 is formed on the resist layer 8 by exposure and development, and a layer of a magnetic material (i.e., the upper core layer 6) is formed by plating on the undercoat layer 7 that is exposed through the formed pattern. After the plating, by removing the resist layer 8 remained, the upper core layer 6 is completed as shown in FIG. 30.
However, the conventional thin-film magnetic head has accompanied the following problems in forming the upper core layer 6 from the structural point of view.
As shown in FIG. 31, since the insulating layer 9, the coil layer 4 and the insulating layer 5 are formed on the lower core layer 1 one above another, the layered films are heaped from the surface of the lower core layer 1 with a thickness H3. Therefore, the resist layer 8 has a very large film thickness H1 in an area of the lower core layer 1 on which the coil layer 4, etc. are not formed, i.e., in a part of the resist layer 8 which is formed on the lower core layer 1 near its fore end. On the contrary, the resist layer 8 formed on the insulating layer 5 has a small film thickness H2.
For that reason, it is hard to precisely adjust the depth of a focus in the steps of exposure and development for patterning the resist layer 8, thus resulting in a difficulty in forming the pattern of the upper core layer 6 in a predetermined shape on the resist layer 8 and hence deterioration of pattern accuracy.
In particular, as described above, the fore end portion 6a of the upper core layer 6 is formed to have a width equal to the track width Tw. To realize a higher recording density in future, the track width Tw must be realized at a smaller value.
Further, as described above, the film thickness H1 of a portion of the resist layer 8, in which the fore end portion 6a of the upper core layer 6 is to be formed, is very large. The large depth of a focus is therefore required in the steps of exposure and development to form a pattern in the portion of the resist layer 8 having the film thickness Hi. However, the large depth of a focus deteriorates resolution, and the fore end portion 6a of the upper core layer 6 is formed with a width larger than the track width Tw of a predetermined size.
Moreover, because of a heap defined by the insulating layers 5, 9 and the coil layer 4 which are formed on the lower core layer 1, the film thickness H1 of the resist layer 8 is not uniform and an adverse effect such as diffused reflection is more likely to occur during exposure and development. It is hence impossible to form the upper core layer 6 into a predetermined shape. Particularly, it is impossible to form the fore end portion 6a of the upper core layer 6 so as to have a width equal to the track width Tw of a predetermined size.
To overcome the above-mentioned problems, there is proposed, for example, a method of forming the insulating layers 5, 9 and the coil layer 4 at a position shifted in the height direction (Y-direction as indicated in the drawings), and increasing a length T1 of the area of the lower core layer 1 near its fore end on which the coil layer 4, etc. are not formed. Thus, the method is intended to form the fore end portion 6a of the upper core layer 6 to have a width, which is equal to the predetermined track width Tw, by reducing the film thickness of the resist layer 8 formed on the area of the length T1 to a value smaller than in the case shown in FIG. 31.
Even with the above-mentioned method, however, it is unavoidable that the film thickness of the resist layer 8 is not uniform. Accordingly, a difficulty still remains in forming the upper core layer 6 into a predetermined shape due to such an adverse effect as diffused reflection occurred during exposure and development.
Further, when the coil layer 4, etc. are formed at a position shifted in the height direction (Y-direction as indicated in the drawings), the fore end portion 6a of the upper core layer 6 can be formed to have a larger length. However, since the fore end portion 6a of the upper core layer 6 is in the elongate form of the track width Tw, magnetic saturation is more likely to occur in the fore end portion 6a, and deterioration of the OW characteristic is caused.
The term xe2x80x9coverwritexe2x80x9d means an operation of writing data over data previously written in the same position. The OW characteristic is evaluated by the steps of recording data at low frequency, overwriting the recorded data with new data at high frequency, and measuring how much a remaining output of a recording signal at the low frequency has reduced from an original output of the recording signal at the low frequency as obtained before overwriting with the new data at the high frequency.
With the view of overcoming the problems set forth above, the present invention provides a thin-film magnetic head and a method of manufacturing the head, which enables an upper core layer to be formed into a predetermined shape, and can improve an overwrite characteristic and suppress the occurrence of write fringing.
A thin-film magnetic head according to the present invention comprises a lower core layer, an upper core layer positioned in an opposing relation to the lower core layer through a nonmagnetic gap layer at a head surface facing a recording medium, the magnetic head further comprising a lower magnetic pole layer being formed on the lower core layer to extend from the head surface facing the recording medium over a predetermined length in a height direction, the gap layer contacting the lower magnetic pole layer; and a coil layer and a coil insulating layer being formed in a space corresponding to a level difference between the lower magnetic pole layer and the lower core layer, the coil insulating layer filling spaces defined at a pitch of conductors of the coil layer between the conductors; an upper surface of the coil insulating layer or upper surfaces of both the coil insulating layer and the coil layer being leveled flush with a reference plane, which is assumed to be defined by a junction surface between the lower magnetic pole layer and the gap layer, so that a flat surface extends in the height direction along the reference plane, the upper core layer having a portion exposed at the head surface facing the recording medium and contacting the gap layer at a track width Tw.
An main object of the present invention is to form the upper core layer into a predetermined shape. To achieve the object, particularly, a position in which the coil layer is formed is changed from that in a conventional magnetic head.
In the conventional magnetic head, a coil layer is formed on a gap layer. With such a structure, the coil layer, etc. cannot be avoided from heaping to a large extent from the gap layer when formed on it. It is therefore difficult to form the upper core layer with high pattern accuracy within a satisfactory allowance.
The inventors found that the upper core layer can be formed with high pattern accuracy by forming the coil layer under the gap layer.
The thin-film magnetic head according to the present invention has structural features as follows. In the magnetic head of the present invention, the lower magnetic pole layer is formed on the lower core layer. The coil layer and the coil insulating layer are formed in the space corresponding to the level difference between the lower magnetic pole layer and the lower core layer.
Further, assuming the junction surface between the lower magnetic pole layer and the gap layer to be a reference plane, an upper surface of the coil insulating layer or upper surfaces of both the coil insulating layer and the coil layer, which are formed in the aforesaid space, are leveled flush with the reference plane, and a flat surface is formed to extend in the height direction along the reference plane.
Since the gap layer is formed to extend over the flat upper surfaces of the lower magnetic pole layer and the flat upper surface of the coil insulating layer or the flat upper surfaces of both the coil insulating layer and the coil layer. Therefore, the gap layer also has a flat upper surface.
Then, in the present invention, the upper core layer can be directly formed on the flat upper surface of the gap layer, and a surface on which the upper core layer is to be formed includes neither projections nor recesses which have been present in the conventional magnetic head. Accordingly, a resist layer used for forming the upper core layer can be formed with a reduced and uniform film thickness, and an adverse effect such as diffused reflection can be prevented from occurring during exposure and development. As a result, the upper core layer can be formed with high pattern accuracy. In particular, a fore end portion of the upper core layer exposed at the head surface facing the recording medium can be high-accurately formed with the track width Tw of a predetermined size.
Also, since the upper core layer is formed on the flat surface, the fore end portion of the upper core layer, which is formed with the track width Tw, can be formed to have a shorter length. It is hence possible to avoid magnetic saturation near the fore end of the upper core layer, to reduce attenuation of magnetic flux density, and to improve the OW characteristic.
In the present invention, preferably, the gap layer sandwiched between the upper core layer and the lower magnetic pole layer is formed with the track width Tw, and the lower magnetic pole layer includes a projected portion contacting the gap layer and having a width equal to the track width Tw. In this case, preferably, slopes inclining in directions away from the upper core layer are formed to extend from a base end of the projected portion at upper surfaces of the lower magnetic pole layer on both sides of the projected portion. With these features, the occurrence of write fringing can be suppressed.
Also, in the present invention, the lower magnetic pole layer may be formed integrally with the lower core layer.
Further, preferably, a lift layer is formed on a rear end portion of the lower core layer and an upper surface of the lift layer is positioned flush with the reference plane, the lift layer contacting a base end portion of the upper core layer. By forming the lift layer, magnetic coupling between the lower core layer and the upper core layer can be easily established, and the manufacture of the thin-film magnetic head can be facilitated.
The lift layer may be formed integrally with the lower core layer.
Preferably, the coil insulating layer is formed of an inorganic insulating material.
In the present invention, the surfaces flush with the reference plane are surfaces flattened by trimming. As described later in more detail in connection with the manufacturing method, the surfaces flush with the reference plane are obtained by polishing using the CMP technology, for example.
Preferably, an insulating undercoat layer is formed between the coil layer and the lower core layer. This feature enables a dielectric withstand voltage between the coil layer and the lower core layer to be improved.
The thin-film magnetic head of the present invention may further comprise an upper magnetic pole layer formed on the gap layer to extend from the head surface facing the recording medium over a predetermined length in the height direction, the upper magnetic pole layer having a portion exposed at the head surface facing the recording medium and formed with the track width Tw; and a second coil layer being electrically connected to the coil layer and introducing a recording magnetic field to the lower core layer and the upper core layer, and a second coil insulating layer filling spaces defined at a pitch of conductors of the second coil layer between the conductors, the second coil layer and the second coil insulating layer being formed on the gap layer to locate in an area extending from the upper magnetic pole layer in the height direction; the upper core layer being joined onto the upper magnetic pole layer at a position spaced from the head surface facing the recording medium in the height direction.
The above features represent the coil layer having a two-layered structure. By employing the two-layered structure, the coil layer can be formed with a smaller width, and the length of a magnetic path established through the lower core layer and the upper core layer can be reduced. It is therefore possible to achieve a reduction of inductance and to manufacture a thin-film magnetic head adaptable for an increase of the recording density in future.
Also, in the thin-film magnetic head having the above features, the upper magnetic pole layer is formed on the gap layer, and has a portion which is exposed at the head surface facing the recording medium and is formed with the track width Tw. Since the upper magnetic pole layer is directly formed on the flat upper surface of the gap layer, the upper magnetic pole layer can be formed to have the track width Tw of a predetermined size with high accuracy.
Further, the upper core layer formed on the upper magnetic pole layer is extended in the height direction from a position spaced from the head surface facing the recording medium so that the upper core layer is not exposed to the head surface facing the recording medium.
With such an arrangement, there is no longer a need of forming the upper core layer so as to have a fore end portion with the track width Tw, and the upper core layer serves only to couple a magnetic path between the upper magnetic pole layer and the lower core layer. From the viewpoint of avoiding magnetic saturation, therefore, the upper core layer is preferably formed with a width larger than the track width Tw.
As a result, even when the surface on which the upper core layer is to be formed is heaped to some extent, the upper core layer having a relatively large width can be formed into the predetermined shape with high pattern accuracy.
Additionally, since the upper core layer is formed on the upper magnetic pole layer to extend from a position spaced away from the surface facing the recording medium in the height direction, the occurrence of write fringing can be suppressed.
In the present invention, preferably, the upper magnetic pole layer comprises a fore end portion formed with the track width Tw, and a rear portion formed to extend from a base end of the fore end portion in the height direction with a width gradually increasing, the upper core layer being joined onto the rear portion of the upper magnetic pole layer.
Further, assuming a junction surface between the upper magnetic pole layer and the upper core layer to be a second reference plane, an upper surface of the second coil insulating layer or upper surfaces of both the second coil insulating layer and the second coil layer may be leveled flush with the second reference plane so that a flat surface extends in the height direction along the second reference plane.
In that case, preferably, the second coil insulating layer is formed of an inorganic insulating material. Also, the surfaces flush with the second reference plane are surfaces flattened by trimming.
With the above features, the upper core layer can be formed on a part of the upper magnetic pole layer and the upper surface of the second coil insulating layer or the upper surfaces of both the second coil insulating layer and the second coil layer with higher pattern accuracy.
The second coil insulating layer may be formed of an organic insulating material. In this case, since the second coil insulating layer is heaped from the second reference surface to some extent, the upper core layer cannot be formed on a perfectly flat surface. However, the upper core layer can be formed into the predetermined shape even with slightly reduced accuracy as mentioned above, and hence such a heap does not significantly affect the pattern formation of the upper core layer.
Preferably, when a lift layer is not formed on the lower core layer, a second lift layer is formed to rise from the lower core layer, and when a lift layer is formed on the lower core layer, the second lift layer is formed on the lift layer, a base end portion of the upper core layer being formed in contact with an upper surface of the second lift layer. These features enable the lower core layer and the upper core layer to be magnetically connected to each other with more ease.
The present invention also provides a method of manufacturing a thin-film magnetic head comprising a lower core layer, an upper core layer positioned in an opposing relation to the lower core layer through a nonmagnetic gap layer at a head surface facing a recording medium, and a coil layer for introducing a recording magnetic field to the lower core layer and the upper core layer, the method comprising the steps of (a) forming a lower magnetic pole layer on the lower core layer to extend from the head surface facing the recording medium over a predetermined length in a height direction; (b) forming an insulating undercoat layer on the lower core layer; (c) forming a coil layer and a coil insulating layer on the insulating undercoat layer, the coil insulating layer filling spaces defined at a pitch of conductors of the coil layer between the conductors; (d) trimming an upper surface of the coil insulating layer or upper surfaces of both the coil layer and the coil insulating layer to be flush with a reference plane, which is assumed to be defined by the upper surface of the lower magnetic pole layer, so that a flat surface extends in the height direction along the reference plane; (e) forming a gap layer on the upper surface of the lower magnetic pole layer and the flat surface; and (f) forming an upper core layer on the gap layer by patterning, the upper core layer having a portion exposed at the head surface facing the recording medium and having a width equal to a track width Tw.
Thus, in the manufacturing method of the present invention, the lower magnetic pole layer is formed on the lower core layer in the step (a), and the coil layer and the coil insulating layer are formed in a space corresponding to a level difference between the lower core layer and the lower magnetic pole layer in the step (c).
Further, in the step (d), the upper surface of the coil insulating layer or the upper surfaces of both the coil layer and the coil insulating layer are leveled using the CMP technology, for example, to be flush with the reference plane (i.e., the upper surface of the lower magnetic pole layer), so that a flat surface extends in the height direction along the reference plane. Then, the gap layer is formed on the upper surface of the lower magnetic pole layer (reference plane) and the flat surface. This enables the upper core layer to be formed on the gap layer having a flat upper surface. Accordingly, a resist layer used for forming the upper core layer can be formed with a reduced film thickness, and an adverse effect such as diffused reflection can be prevented from occurring during exposure and development. As a result, the upper core layer can be formed with high pattern accuracy. In particular, a portion near a fore end of the upper core layer can be formed to have a width equal to the track width Tw of a predetermined size. A thin-film magnetic head adaptable for a narrower track width can be manufactured.
In the manufacturing method of the present invention, preferably, the step (a) includes a step of forming a lift layer of a magnetic material on the lower core layer on the side away from the head surface facing the recording medium, the step (d) includes a step of trimming an upper surface of the lift layer to be flush with the reference plane, and the step (f) includes a step of joining a base end portion of the upper core layer to the upper surface of the lift layer. By forming the lift layer, magnetic coupling between the upper core layer and the lower core layer can be easily established, and the manufacture of the thin-film magnetic head can be facilitated.
Also, preferably, the step (a) includes a step of forming the lower magnetic pole layer on the lower core layer by frame plating, and a step of, when a lift layer is also formed on the lower core layer, forming the lift layer by the frame plating at the same time as forming the lower magnetic pole layer.
In the above case, preferably, the manufacturing method further comprises a step of filling surroundings of the lower core layer by an insulating layer prior to forming the lower magnetic pole layer or both the lower magnetic pole layer and the lift layer, and a step of leveling upper surfaces of the lower core layer and the insulating layer to be flush with each other.
Further, in the manufacturing method of the present invention, the step (a) may include a step of protecting an area of the upper surface of the lower core layer on which the lower magnetic pole layer is to be formed, and then trimming a remaining area of the upper surface of the lower core layer, thereby forming the lower magnetic pole layer to project from the lower core layer, or a step of, when a lift layer is also formed on the lower core layer, protecting areas of the upper surface of the lower core layer on which the lower magnetic pole layer and the lift layer are to be formed, and then trimming a remaining area of the upper surface of the lower core layer, thereby forming the lower magnetic pole layer and the lift layer to project from the lower core layer.
In the above case, preferably, the manufacturing method further comprises a step of filling surroundings of the lower core layer by an insulating layer prior to forming the lower magnetic pole layer or both the lower magnetic pole layer and the lift layer, and a step of leveling the upper surfaces of the lower core layer and the insulating layer to be flush with each other.
Preferably, the manufacturing method of the present invention further comprises, subsequent to the step (f), steps of (g) removing portions of the gap layer which are extended from a junction surface between the upper core layer and the gap layer on both sides of the upper core layer formed with the track width Tw; (h) trimming the upper surfaces of the lower magnetic pole layer that have been exposed by removing the portions of the gap layer so that a junction surface between the lower magnetic pole layer and the gap layer has a width equal to the track width Tw, thereby forming a projected portion of the lower magnetic pole layer to extend in a direction toward the upper core layer; and (i) a step of forming slopes to extend from a base end of the projected portion at the upper surfaces of the lower magnetic pole layer on both sides of the projected portion, the slopes inclining in directions away from the upper core layer.
By employing the above-mentioned steps, a thin-film magnetic head capable of realizing a narrower track width and suppressing the occurrence of write fringing can be manufactured.
Preferably, the coil insulating layer filling the spaces defined at a pitch of conductors of the coil layer between the conductors is formed of an inorganic insulating material. This feature enables the upper surface of the coil insulating layer to be satisfactorily polished using the CMP technology, for example.
Moreover, instead of the step (f), the manufacturing method of the present invention preferably comprises (j) forming an upper magnetic pole layer on the gap layer to extend from the head surface facing the recording medium over a predetermined length in the height direction, the upper magnetic pole layer having a portion exposed at the head surface facing the recording medium and formed with the track width Tw; (k) forming a second coil layer and a second coil insulating layer on the gap layer to extend from the upper magnetic pole layer in the height direction, the second coil insulating layer filling spaces defined at a pitch of conductors of the second coil layer between the conductors; and (l) joining the upper core layer onto the upper magnetic pole layer at a position spaced from the head surface facing the recording medium in the height direction.
With the above manufacturing method, the coil layer can be formed of a two-layered structure. Therefore, the coil layer can be formed with a smaller width, and the length of a magnetic path established through the lower core layer and the upper core layer can be reduced.
Also, the upper magnetic pole layer can be formed on the flat upper surface of the gap layer, and the fore end portion of the upper magnetic pole layer can be formed to have a width equal to the track width Tw of a predetermined size with high accuracy.
Further, by forming the upper core layer on the upper magnetic pole layer to extend from the position spaced from the head surface facing the recording medium in the height direction, the upper core layer can be formed with a width larger than the track width Tw. Accordingly, even when the surface on which the upper core layer is to be formed is heaped to some extent, the upper core layer can be formed into the predetermined shape with more ease.
Preferably, the step (j) includes a step of forming the upper magnetic pole layer by forming a fore end portion with the track width Tw, and forming a rear portion to extend from a base end of the fore end portion in the height direction with a width gradually increasing, and the step (l) includes a step of joining the upper core layer onto the rear portion of the upper magnetic pole layer.
Further, the step (k) may include a step of trimming an upper surface of the second coil insulating layer or upper surfaces of both the second coil layer and the second coil insulating layer to be flush with a second reference plane, which is assumed to be defined by the upper surface of said upper magnetic pole layer, so that a flat surface extends in the height direction along the second reference plane. In this case, preferably, the second coil insulating layer filling the spaces defined at a pitch of conductors of the second coil layer between the conductors is formed of an inorganic insulating material.
The above step can be realized by using, e.g., the CMP technology. By leveling the upper surface of the second coil insulating layer or the upper surfaces of both the second coil layer and the second coil insulating layer to be flush with the second reference plane (i.e., the upper surface of the second coil insulating layer), the upper core layer can be formed on the second reference surface in the predetermined shape with high pattern accuracy.
The second coil insulating layer filling the spaces defined at a pitch of conductors of the second coil layer between the conductors may be formed of an organic insulating material.
In addition, preferably, the step (j) includes a step of forming a second lift layer on a lift layer when the lift layer is formed on the lower core layer, or on the lower core layer when the lift layer is not formed on the lower core layer, and the step (l) includes a step of joining a base end portion of the upper core layer onto the second lift layer.
In the above steps, the second lift layer is formed on the lift layer which is formed on the lower core layer, or on the lower core layer. By employing those steps, when the coil layer is of the two-layered structure, magnetic coupling between the upper core layer and the lower core layer can be easily established, and the manufacture of the thin-film magnetic head can be facilitated.